1. Field of the Invention
This invention relates to a test device for the detection and measurement of chemical emissions to the atmosphere.
2. Description of Related Art
Industrial components, especially in aging plants, are highly susceptible to gas leaks and the escape of chemical emissions to the atmosphere. As a result, leak detection and measurement is an important safety and cost-saving tool within industrial plants.
A common method that is still employed for detecting leaks is covering a suspect component in soapy water to identify the leak. Alternatively, xe2x80x9csnifferxe2x80x9d devices that use a flame ionization detector (FID) or other sensor to detect leaking gas can be used to find and identify the presence of a leak. FIDs are of limited utility for components that are leaking heavily in that if the gas emissions exceed 90,000 ppm the FID xe2x80x9cflames outxe2x80x9d and must be reset. Neither of the above-described methods is capable of measuring the quantity of the gas emitted but only the concentration of the emitted gas in a plume. Because the concentration of the emitted gas varies significantly with speed and direction of wind, the angle of the probe, the distance of the probe from the leak, the geometry of the leaking component and the flow rate of the sample through the instrument, attempts to correlate the leak rate with the concentration have been unsuccessful. Studies have shown that the scatter in the correlation of leak rate and concentration is 3 to 4 orders of magnitude. Therefore, by using a concentration measurement to determine leak rate, the leak could be calculated at any number between 1 cf per day and 10,000 cf per day.
Early methods for quantification involved bagging a leak and sending the bagged specimen to an off-site lab for testing. This process was time consuming and therefore very expensive. Later, components were bagged and a semi-mobile test device analyzed the sample at the test site.
As taught in Howard, U.S. Pat. No. 5,563,335, a test device was later conceived that drew in an air sample through a sample hose at a high flow rate so as to capture the entire leak and thereupon analyze the concentration of gas emissions within the air sample. By measuring both the concentration in the sample and the concentration in the background air, measurement of the leak rate may be obtained.
It is one object of this invention to provide a test device wherein air is drawn directly into a housing without passing through a sample hose thereby reducing frictional losses and the possibility for static charge build-up.
It is another object of this invention to provide a test device that corrects for contaminants in the background air as well as for interference from other leaks.
It is still another object of this invention to provide a test device that functions as both a leak detector and a leak quantifier.
It is yet another object of this invention to provide a test device that requires a minimal amount of input from an operator to generate useable test data.
A test device for measuring chemical emissions to the atmosphere according to one preferred embodiment of this invention preferably includes a static resistant housing for portable containment of the components of this invention.
An air mover, such as a fan, is positioned within the housing or can be located on the person of the operator such as a belt or backpack and may be connected to the housing with a hose. The fan is arranged to draw ambient air directly into the housing. A spark-proof motor is connected to the air mover and capable of operation at two or more speeds. An anemometer is positioned within the housing, preferably downstream of the air mover, for detecting a flow rate of air through the housing, as generated by the air mover.
A sampling head for detecting the presence of a chemical emission is positioned in communication with the housing, preferably within the housing. The sampling head preferably comprises a mixing element and a detector.
A calculator is connected in communication with the anemometer and the sampling head and measures the concentration of the chemical emissions from the leaking component. The calculator preferably comprises a computer or logic board that calculates the leak rate of the chemical emissions from the leaking component based upon several pre-programmed parameters.
A signal indicator is also positioned with respect to the housing and indicates to the operator whether a leak is detected. Once a leak is detected, according to one preferred embodiment of this invention, the test device is switched from a survey mode for identifying the presence of a leak to a quantification mode for measuring the leak rate of the leak from the component.
The test device may also include one or more of a volume display showing the volume of air passing through the housing; a chemical display showing the chemical emission content of the air passing through the housing; a leak display showing the total chemical emission rate; and/or a mode display showing whether the test device is in a surveying mode or a quantifying mode.
Preferably, the test device is operated with the air mover set at a low flow rate during the survey mode. When the presence of a leaking component is detected, the test device is set to draw air directly into the housing at a high flow rate during the quantification mode. The calculator thereupon determines the leak rate from the concentration of the chemical emission drawn through the housing and the flow rate measured by the anemometer. The calculator changes the flow rate and then recalculates the leaks rate. The calculator then uses the two leak rate values in an internal algorithm to determine whether the calculated leak rate is accurate; whether the entire leak was captured; and/or the presence or absence of the chemical in the background air. The test device thereby signals whether the test result is sufficient or whether the test result is unreliable based upon the presence of interference from another leaking component, presence of the chemical in the background air or incomplete capture of the leak. If the test result is unreliable, based upon the signal received, the operator can run another test from a different location near the leaking component.
The calculator may also calculate concentration, flow rate and leak rate by manipulating the output of the test device by several pre-programmed calculation factors. The calculator may additionally convert output data to digital values and calculate average values over specified time periods. Further, the calculator may control the operation of the test device during an automatic mode and provide signals to the operator during all modes. Finally, the calculator may record the accumulated data in a data logger and allow the accumulated data to be downloaded to a computer, such as a PC.